Non-circular electrical cable having a reduced pulling force

ABSTRACT

In various embodiments, a non-circular electrical cable having a reduced pulling force attributable to the exterior surface of an outer sheath, and method of producing the same is provided. In various embodiments, an outer sheath of the cable may comprise a first and second sheath layer, the second sheath layer being located external to the first sheath layer, and comprising a nylon material configured to reduce the pulling force necessary for installing the cable. In various embodiments, the first sheath layer may be extruded using a tube extrusion method into a substantially circular shape, and the second sheath layer may be extruded using a pressure extrusion methods onto the exterior surface of the first sheath layer while maintaining the at least substantially circular shape of the sheath. The sheath may then be pulled onto the surface of a plurality of conductors to form the non-circular electrical cable.

BACKGROUND

Non-metallic sheathed cable, such as NM-B type cable, is often used for providing electrical systems within residential structures. Known non-metallic sheathed cable assemblies often comprise one or more electrical conductors individually coated in an electrical insulator (e.g., a solid or stranded copper wire coated in a plastic material) bundled together and collectively sheathed in a non-metallic outer sheath. Generally the non-metallic outer sheath comprises a non-conductive polymer such as poly-vinyl chloride (PVC) and has been understood to provide mechanical protection for the bundled wires against insulation tears and abrasion.

During installation, these cables often must be threaded through a series of rough-hewn holes cut through wooden floor and ceiling joists, headers, and wall studs (such as those commonly referred to as 2×4s, 2×6s, 2×8s, and/or the like) or through narrow plastic conduit. Due to time pressures involved in installing electrical cable and the often complex shapes of walls and structures included in residential buildings, the electrical cable installation path comprises a substantially non-linear path through multiple wooden studs. These cable installation paths often run substantially horizontally through a series of wooden wall studs, turn around corners to follow additional path segments substantially perpendicular to previous segments, and turn vertically to run along the length of wooden wall studs to electrical outlets, wall mounted switches, or ceiling mounted light sources.

The exterior surfaces of the non-metallic sheathed cables often have a high dynamic coefficient of friction, and therefore installation of these cables along the installation path may require a substantial pull force to overcome the frictional force occurring between the non-metallic sheathed cable and the surfaces of the installation path while the cable is being pulled. In some installations, the pulling force necessary to move the cable through the installation path may be high enough to deform or tear the outer non-metallic sheath. Therefore, when installing long segments of non-metallic sheathed cable, multiple installers may be necessary to thread the non-metallic sheathed cable along the installation path. A first installer may be necessary to push lengths of cable into the installation path, and one or more additional installers may be necessary to pull the provided lengths of cable along the installation path.

Electricians and installers have previously coated non-metallic sheathed cables with a separate cable lubricant, often in the form of a liquid or gel, at the installation site to reduce the coefficient of friction of non-metallic sheathed cables. Applying these separate cable lubricants at the job site may require additional installation time, can be messy, and, depending on the chemical composition of the lubricant, may negatively impact the mechanical and insulative properties of the non-metallic sheath.

As noted in U.S. Pat. No. 7,411,129 to Kummer et al., incorporated herein by reference, and patents and patent applications related thereto, advances have been made in decreasing the pulling force necessary to install electrical conductors in substantially non-linear installation paths. These advances include sheath formulations wherein nylon or another polymer is mixed with a lubricant and formed over the outside of the conductor in order to decrease the surface coefficient of friction. However, these efforts have been directed to generally circular conductors, such as circular Thermoplastic High Heat Resistant Nylon (THHN) wiring or the like.

In many residential installations, however, substantially flat or non-circular cables, such as Southwire's Romex® 14/2, 12/2, or 10/2 cable, are used for a substantial portion of electrical wiring. Such cable may comprise two separately insulated conductors and a separate ground wire arranged in a substantially flat arrangement (e.g., the center point of each of the three wires are nominally aligned in a single plane). The three wires are encapsulated in a non-metallic outer sheath as described above. As noted herein, previous attempts to decrease the pulling force necessary for installation of non-metallic sheathed cables have been limited to circular wires and cables. Physical characteristics of the materials utilized in the reduction of the surface coefficient of friction for non-metallic sheathed cables have previously limited the commercial manufacture of previously known methods and materials to circular cables and wires. Moreover, product safety and certification organizations, such as the Underwriters Laboratory (UL), have implemented sheath thickness and uniformity standards for non-metallic sheathed cables, highlighting the importance of a uniform sheath thickness. Therefore, new manufacturing methods are needed to consistently produce non-circular, non-metallic sheathed cable with a reduced surface coefficient of friction in order to decrease the pull force necessary to install these cables in generally non-linear cable installation paths.

BRIEF SUMMARY

Various embodiments of the present invention are directed to a process for producing non-circular electrical cable, wherein the non-circular electrical cable comprises one or more conductors arranged in a non-circular arrangement and an exterior sheath comprising a first sheath layer and a second sheath layer. A process according to various embodiments of the present invention comprises steps for: (1) advancing conductors through an extruder head, (2) extruding a first sheath layer comprising a plastic material around the conductors, wherein the first sheath layer is initially extruded in a substantially circular shape having an inner surface and an exterior surface and at least a portion of the inner surface thereof is spaced from the conductors, (3) extruding a second sheath layer comprising a nylon material onto the exterior surface of the first sheath layer, (4) applying a negative pressure to the interior surface of the first sheath layer, thereby pulling the first sheath layer and second sheath layer onto the conductors and into a non-circular shape having a cross section substantially similar to the combined cross section of the one or more conductors, and (5) cooling the first and second sheath layers. In various embodiments, the second sheath layer may additionally comprise a lubricant for decreasing the pull force of the cable.

In addition, various embodiments of the present invention are directed to a non-circular electrical cable comprising one or more conductors arranged in a non-circular arrangement and an exterior sheath loosely surrounding the conductors having a non-circular cross-section, the exterior sheath comprising a first sheath layer and a second sheath layer. In various embodiments, the first sheath layer has an exterior surface and an interior surface, and comprises a plastic material. In various embodiments, the second sheath layer may have an exterior surface and an interior surface, and comprises a polyamide, such as a nylon material. Additionally, the second sheath layer may comprise a lubricant for decreasing the pull force of the cable.

Yet other embodiments of the present invention are directed to a non-circular electrical cable comprising one or more conductors arranged in a non-circular arrangement and an exterior sheath loosely surrounding the conductors having a non-circular cross-section, the exterior sheath comprising a first sheath layer and a second sheath layer. In various embodiments, the first sheath layer has an exterior surface and an interior surface, and comprises a plastic material. In various embodiments, the second sheath layer may have an exterior surface and an interior surface, and comprises a polyolefin (e.g., polypropylene). Additionally, the second sheath layer may comprise a lubricant for decreasing the pull force of the cable.

Yet other embodiments of the present invention are directed to a non-circular electrical cable comprising one or more conductors arranged in a non-circular arrangement and an exterior sheath loosely surrounding the conductors having a non-circular cross-section, the exterior sheath comprising a first sheath layer and a second sheath layer. In various embodiments, the first sheath layer has an exterior surface and an interior surface, and comprises a plastic material. In various embodiments, the second sheath layer may have an exterior surface and an interior surface, and comprises a polyester. Additionally, the second sheath layer may comprise a lubricant for decreasing the pull force of the cable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 shows an exemplary schematic of a system utilized to produce non-metallic sheathed cable according to one embodiment of the present invention;

FIG. 2 shows an exemplary schematic of various components present within an extruder head, according to one embodiment of the present invention;

FIGS. 2A-A and 2B-B show exemplary cross sectional views of a sheathed cable at various points during the manufacturing process, according to one embodiment of the present invention;

FIG. 3 shows a cutaway view of a sheathed cable according to one embodiment of the present invention;

FIGS. 4A and 4B show components of a pull force test apparatus according to various embodiments of the present invention; and

FIG. 4C illustrates a threading pattern for threading a cable to be tested using the testing apparatus according to various embodiments of the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Referring initially to FIG. 1, there is depicted a schematic diagram of exemplary equipment 1 utilized to produce an electrical cable according to one embodiment of the present invention. As shown in FIG. 1, multiple conductors 2 a, 2 b, 2 c may be combined to create a multi-conductor cable. In various embodiments, the conductors may comprise multiple insulated conductors 2 a, 2 c and one bare conductor 2 b. For example, various embodiments may comprise two 12-gauge insulated conductors and one 12-gauge bare ground wire and may be commonly referred to as “12/2 wire.” Each insulated conductor may comprise a conductive element surrounded by an insulating material. The insulating material may, in certain embodiments, comprise an extruded polymer material such as PVC, a nylon material, and/or other materials having electrical insulative properties. In various embodiments, the PVC may be a foamed PVC material or a re-grind PVC material obtained from recycled PVC products. Although illustrated as comprising three conductors, it will be understood by those skilled in the art that any number of conductors may be utilized herein.

Referring again to FIG. 1, the multiple conductors 2 a, 2 b, 2 c may, in various embodiments, be stored using wire storage devices illustrated in FIG. 1 as a plurality of spools 3 a, 3 b, 3 c. It will be understood by those skilled in the art that any of a variety of wire storage devices may be utilized, including cages, barrels, pallets, and/or the like. The multiple conductors 2 a, 2 b, 2 c may be removed from the wire storage devices during the electrical cable production process as needed, and supplied to an extrusion head 4 during production. Although not shown in FIG. 1, dam paper 28 and/or a paper barrier 29 may also be supplied to the extrusion head 4 in various embodiments. The equipment may additionally include a polyamide-supply tank 5 containing a polyamide 6 (e.g., nylon) used to form a second sheath layer 26 of a resulting cable 13 having a reduced pull force. As illustrated in FIG. 1, the polyamide 6 is illustrated as a plurality of polyamide pellets, however other polyamide forms may be utilized. The polyamide 6 may be supplied to the extruder head 4 during production via a polyamide-supply conduit 7. In various embodiments, the equipment may additionally include an additive-supply tank 8 containing an additive composition 9 (e.g., a fire retardant and/or a lubricant) that may be combined and mixed with the polyamide 6 prior to supplying the resulting mixture to the production process. As a non-limiting example, the additive composition 9 may comprise a lubricant, such as erucamide, a silicon-based material (e.g., a silicon oil), and/or the like configured to further reduce the pull force of the cable attributable to the resulting second sheath layer 26. In various embodiments, the additive composition 9 may be supplied to the polyamide-supply tank 5 where it is mixed with the polyamide 6 to create a substantially homogenous mixture of polyamide and additive composition via an additive-supply conduit 10. The additive composition 9 also, or alternatively, may be supplied directly to the extruder head 4, where it may be combined with the polyamide 6 prior to and/or during an extrusion process. In such a configuration, an extruder (e.g., a twin-screw extruder, not shown) is provided just upstream of the extrusion head 4 and is configured to pressurize, heat, and combine the polyamide 6 and additive 9 in a molten state prior to extruding the combined material. The polyamide 6 and additive 9 may be provided to the extruder in pellet form or molten form.

The equipment 1 may additionally include an insulator-supply tank 11 containing an insulator material 12 configured to supply the insulator material 12 to the extruder head 4 via an insulator-supply conduit 11 a. In various embodiments, the insulator material 12 may comprise a plastic material having electrical insulative properties, such as PVC, and may be supplied to the extruder in pelletized form or in a molten state. In various embodiments, at least a portion of the PVC may be a re-grind PVC material obtained from recycled PVC products. As illustrated in FIG. 1, the insulator material 12 may be stored in the insulator-supply tank 11 as a plurality of insulator pellets, however the insulator material 12 may be stored in a variety of forms. In various embodiments, the insulator material 12 may be supplied to the extruder head 4 at a location upstream from the polyamide 6 supply location via the insulator-supply conduit 11 a. In various embodiments, the insulator supply conduit 11 a may comprise an extruder (e.g., a single-screw extruder, not shown) configured to pressurize and heat the insulator material 12 prior to supplying the insulator material to the extruder head 4. The insulator material 12 may also, or alternatively, be foamed as part of the extrusion process, such that the overall density of the insulator material is reduced. As will be described in greater detail herein, the polyamide 6, additive composition 9, and insulator material 12 may be applied to the conductors in the extruder head 4, such that the resulting cable 13 comprises the multiple conductors 2 a, 2 b, 2 c, surrounded by a multi-layer sheath having at least a first sheath layer 27 comprising the insulator material 12 and a second sheath layer 26 that may comprise the composition of polyamide 6 and additive 9. With the additive 9, the exterior surface of the resulting cable 13 comprises the second sheath layer 26 which results in a cable having a reduced pull force relative to the prior art, thus reducing the pulling force necessary for installing the cable 13 in an installation location.

In various embodiments, the equipment 1 may comprise a cooling box 14 containing a cooling fluid 15. The resulting cable 13 may be fed into the cooling box 14, in order to cool the extruded materials included in the resulting cable 13. The cooling fluid 15 may comprise water, although a variety of alternative cooling fluids may be utilized. The cooled cable 16 may be fed to a cable take-up 17, such as a spool, cage, barrel, and/or the like for transfer and storage. As will be described in greater detail herein, many modifications and other embodiments may be provided according to the terms of this invention. As a non-limiting example, the production process may omit the additive composition 9 entirely, and therefore the equipment 1 may not include the additive-supply tank 8 and additive-supply conduit 10. In various embodiments, the equipment 1 may omit the additive supply tank 8, and the additive composition 9 may be dispersed throughout the polyamide 6, such as a plurality of separate additive composition pellets mixed with the polyamide pellets, or in a plurality of combined pellets, each comprising both polyamide 6 and additive composition 9.

In various embodiments, the polyamide-supply tank 5 may be embodied as a polyolefin-supply tank containing a polyolefin material (e.g., a polypropylene material). In yet other embodiments, the polyamide-supply tank 5 may be embodied as a polyester-supply tank containing a polyester material. In such embodiments, the processing steps described herein in reference to the polyamide-supply tank 5 and polyamide 6 may be performed utilizing the polyolefin-supply tank and polyolefin and/or utilizing the polyester-supply tank and polyester. In such embodiments, the second sheath layer 26 of the resulting cable 13 comprises a polyolefin material and/or a polyester material.

As noted, the polyamide-supply conduit 7 may comprise an extruder assembly (e.g., a twin screw extruder or single screw extruder) configured to heat and supply molten polyamide 6 to the extruder head 4. Similarly, the insulator material supply conduit 11 a may comprise an extruder assembly (e.g., a twin screw extruder or single screw extruder) configured to heat and supply molten insulator material 12 to the extruder head 4.

Extruder Head

Referring now to FIG. 2, the extruder head 4 may comprise a plurality of individual components each configured to facilitate the extrusion of the first sheath layer 27 and second sheath layer 26 onto the multiple conductors 2 a, 2 b, 2 c. In various embodiments, the extruder head 4 may comprise a tip holder 18 having a guide channel 19 extending therethrough. In various embodiments, the guide channel 19 may be sized and shaped such that the multiple conductors 2 a, 2 b, 2 c maintain a predefined orientation as the multiple conductors 2 a, 2 b, 2 c are passed through the extruder head 4. As a non-limiting example, the guide channel 19 may be in a substantially stadium or flat oval shape such that the multiple conductors 2 a, 2 b, 2 c each having a round profile and maintain a nominally flat orientation, such that the center points of each of the multiple conductors 2 a, 2 b, 2 c remain in a single plane. The tip holder 18 may also include one or more vacuum channels 25 extending from the downstream end of the tip holder 18 to a vacuum connection point located in the side of the tip holder 18.

The downstream end of the tip holder 18 may be in contact with an insulator-applicator tip 20. The exterior surface of the insulator applicator tip 20 may be configured to guide molten insulator material 12 into a circular shape around the multiple conductors 2 a, 2 b, 2 c. As a non-limiting example, the exterior surface of the insulator-applicator tip 20 may have a round cross-section. In various embodiments, at least a portion of the exterior surface of the insulator-applicator tip 20 may be substantially frustoconical in shape, such that molten insulator material 12 is guided from a large diameter first end of the insulator-applicator tip 20 to a small diameter second end of the insulator-applicator tip.

The interior surface of the insulator-applicator tip 20 is configured to accept input through the guide channel 19 and the one or more vacuum channels 25. As a non-limiting example, at least a portion of the interior surface of insulator-applicator tip 20 may be at least in part frustoconical in shape, and the second end of the insulator-applicator tip may comprise an exit channel configured to guide the multiple conductors 2 a, 2 b, 2 c through the extrusion head 4. In various embodiments, the exit channel may have at least substantially the same shape as the guide channel 19, such that the orientation of the multiple conductors 2 a, 2 b, 2 c is maintained throughout the extrusion head.

In various embodiments, an insulator material guide (not shown) may be provided near the first end of the insulator-applicator tip 20. The insulator material guide may be configured to direct the molten insulator material 12 onto the exterior surface of the insulator-applicator tip 20 such that an at least substantially uniform flow rate of molten insulator material is provided around the entire circumference of the exterior surface of the insulator-applicator tip.

As installed in the extruder head 4, the second end of the insulator-applicator tip 20 may reside within a first interior portion of an isolator tip 21, the first interior portion of the isolator tip being located on the upstream side of the isolator tip. The exterior surface of the insulator-applicator tip 20 may be spaced away from the first interior surface of the isolator tip 21, such that an insulator channel 22 is formed therebetween.

A second interior portion of the isolator tip 21, located at the downstream side of the isolator tip, may be spaced apart from an exterior surface of a secondary tip 23. In various embodiments, a polyamide channel 24 is formed between the second interior surface of the isolator tip 21 and the exterior surface of the secondary tip 23. As illustrated in FIG. 2, the direction of flow of the polyamide 6 (or a combination of polyamide 6 and additive composition 9) along the polyamide channel 24 may be at least partially opposite the direction of flow of the multiple conductors 2 a, 2 b, 2 c. Therefore, in various embodiments, the second interior surface of the isolator tip 21 may include a redirection portion configured to redirect the molten polyamide into the direction of travel of the multiple conductors 2 a, 2 b, 2 c. In various embodiments, a polyamide guide (not shown) may be provided near an entrance to the polyamide channel 24. The polyamide guide may be configured to direct the molten polyamide 6 into the polyamide channel 24 such that an at least substantially uniform flow rate of molten polyamide (or combination of polyamide 6 and additive composition 9) is provided around the entire circumference of the exterior surface of the secondary tip.

In various embodiments, the extruder head 4 may additionally comprise a heat sink 30 positioned between the insulator channel 22 and polyamide channel 24. Because the polyamide 6 (or combination of polyamide 6 and additive composition 9) may be extruded at a temperature higher than the extrusion temperature of the insulator material 12, the heat sink 30 is configured to prevent the extruder head 4 components adjacent to the insulator material channel 22 from reaching a temperature substantially higher than the insulator material extrusion temperature. In various embodiments, the heat sink 30 may be provided as a metallic ring positioned within a slot formed in the exterior of the isolator tip 21. The metallic material may be different from the material of the remaining components of the extruder head 4 and have high thermal conductivity. As a non-limiting example, the heat sink 30 may comprise a copper material. The heat sink 30 may, in various embodiments, be configured to conduct heat away from the extrusion head 4 and into a second heat sink (not shown) positioned external to the extruder head 4.

Although the various components of the extruder head 4 are illustrated and described herein as having an interior surface and an exterior surface, such terms should not be construed as limiting. As will be understood by those skilled in the art, various embodiments may have alternative orientations. As a non-limiting example, at least one of the insulator channel 22 and the polyamide channel 24 may be oriented such that the respective material flows may be in a direction substantially different from that described herein, with respect to the direction of flow of the multiple conductors 2 a, 2 b, 2 c.

Extrusion Process

Referring now to FIGS. 2, 2A-A and 2B-B, which illustrate a coextrusion process for extruding an outer sheath layer onto the multiple conductors 2 a, 2 b, 2 c, a process for producing an electrical cable according to various embodiments of the present invention will now be described. Such process may be performed continuously, such that a long cable having at least substantially uniform physical properties along the entire length of the cable may be produced. Although FIG. 2 illustrates a coextrusion process, as will be understood by those skilled in the art, a tandem extrusion process may also be used to produce an electrical cable. In various embodiments, the multiple conductors 2 a, 2 b, 2 c may be fed into an upstream end of the extruder head 4, and into a tip holder 18. When being fed into the upstream end of the extruder head 4, the multiple conductors 2 a, 2 b, 2 c may be in a nominally flat configuration, such that a center point of each of the multiple conductors 2 a, 2 b, 2 c are aligned within a single plane. In various embodiments, the multiple conductors 2 a, 2 b, 2 c may be fed through the guide channel 19 extending along the length of the tip holder 18.

Upon exiting the tip holder 18, the multiple conductors 2 a, 2 b, 2 c may enter an interior portion of an insulator-applicator tip 20. Molten insulator material 12 is concurrently fed through the insulator channel 22 at a rate such that the insulator material 12 forms a first sheath layer 27 having an at least substantially circular cross section and a uniform, predefined thickness at substantially the same rate that the multiple conductors 2 a, 2 b, 2 c are fed into the extruder head 4. In preferred embodiments, PVC, heated to a temperature of at least 350 degrees Fahrenheit, may be fed through the insulator channel 22 and extruded using a tube extrusion method around the multiple conductors 2 a, 2 b, 2 c to form a first sheath layer 27. In various embodiments, the first sheath layer 27 may have an at least substantially circular cross section surrounding the multiple conductors 2 a, 2 b, 2 c.

As the multiple conductors 2 a, 2 b, 2 c and first sheath layer 27 are fed into the secondary tip 23, polyamide 6 is concurrently fed through the polyamide channel 24 and onto the surface of the first sheath layer 27, thus forming a second sheath layer 26 thereon. In various embodiments, the polyamide 6 may be combined with an additive composition 9 prior to introduction into the extruder head 4, such that the mixture is extruded to form the second sheath layer 26. The polyamide 6 and additive composition 9 may be fed through the polyamide channel 24 at a rate such that the polyamide and additive composition mixture forms a second sheath layer 26 having a predefined thickness at substantially the same rate that the multiple conductors 2 a, 2 b, 2 c are fed into the extruder head 4. In preferred embodiments, polyamide 6 may be heated to a temperature of at least 500 degrees Fahrenheit and fed through the polyamide channel 24 and extruded onto the exterior surface of the first sheath layer 27 to form the second sheath layer 26. The molten polyamide 6 is extruded onto the surface of the first sheath layer 27, and as the first sheath layer and the polyamide 6 cool, they may mechanically bond together. The resulting combination of the first sheath layer 27 and second sheath layer 26 may have an at least substantially circular cross section surrounding the multiple conductors 2 a, 2 b, 2 c.

The molten polyamide 6 (or combination of polyamide 6 and additive composition 9) may have a low viscosity at the polyamide extrusion temperature. As a predictable, uniform flow rate of molten polyamide around the perimeter of an oval die slot could not be achieved using conventional polyamide extrusion parameters. As a non-limiting example, extruding molten polyamide through a non-circular extrusion die exit to form a second sheath layer 26 may cause an uneven flow rate in the molten polyamide around the perimeter of the extrusion die and thus cause an uneven flow rate in the extrusion direction. Therefore, the resulting second sheath layer 26 may have an inconsistent (non-uniform) thickness around the perimeter of the second sheath layer. However, utilizing an extruder head 4 incorporating a polyamide channel 24 having a circular exit facilitates a uniform flow rate around the perimeter of the circular exit, and the resulting second sheath layer 26 therefore has an at least substantially uniform thickness around the perimeter of the second sheath layer.

As the multiple conductors 2 a, 2 b, 2 c, the first sheath layer 27, and the second sheath layer 26 exit the secondary tip 23, the combination of the first sheath layer 27 and second sheath layer 26 maintains an at least substantially circular cross section with a uniform thickness, while the multiple conductors 2 a, 2 b, 2 c maintain a nominally flat orientation. A cross section showing the relative configurations of the multiple conductors 2 a, 2 b, 2 c, the first sheath layer 27, and the second sheath layer 26 are shown in FIG. 2A-A. As illustrated in FIG. 2A-A, the first sheath layer 27 and second sheath layer 26 each have a uniform thickness around the perimeter of the cross section.

While the multiple conductors 2 a, 2 b, 2 c are fed through the extruder head 4, a negative pressure is applied through the one or more vacuum channels 25 located within the tip holder 18. The negative pressure may be applied in the form of a vacuum, and may be configured such that the combined first sheath layer 27 and second sheath layer 26 are pulled onto the surface of the multiple conductors 2 a, 2 b, 2 c at some distance downstream from the exit of the polyamide channel 24. FIG. 2B-B shows a cross sectional view of an exemplary resulting cable 13, wherein the outer sheath layer has a stadium shape surrounding the multiple conductors 2 a, 2 b, 2 c. As illustrated in FIG. 2B-B, the first sheath layer 27 and second sheath layer 26 of the resulting cable 13 each have a uniform thickness around the perimeter of the cable. A cutaway view of the resulting cable 13 according to various embodiments is shown in FIG. 3A.

Although not illustrated in FIG. 1 or FIG. 2, a dam paper 28 may be fed through the extruder head 4 with the multiple conductors 2 a, 2 b, 2 c. As will be understood by those skilled in the art, the dam paper 28 may be folded around the multiple conductors 2 a, 2 b, 2 c, prior to the multiple conductors entering the tip holder 18. Moreover, at least one conductor 2 b may be individually enclosed in a paper barrier 29 prior to being introduced to the extruder head 4. As will be understood by those skilled in the art, the paper barrier 29 may be folded around the at least one conductor 2 b prior to the at least one conductor entering the extruder head 4.

Non-Circular Electrical Cable Having a Reduced Pull Force

The resulting cable 13 produced according to the above described methods will now be described with reference to FIG. 3. Referring now to FIG. 3, the multiple conductors 2 a, 2 b, 2 c, may be loosely enclosed within a dam paper 28 in a nominally flat orientation, and thus the resulting cable 13 may have a nominally flat shape. Although surrounding the multiple conductors 2 a, 2 b, 2 c such that the dam paper 28 is in contact with the surface of each of the multiple conductors, the dam paper may not be mechanically bonded to the multiple conductors. The combination of the multiple conductors 2 a, 2 b, 2 c and dam paper 28 are enclosed in the outer sheath comprising the first sheath layer 27 and the second sheath layer 26. As described herein, the exterior surface of the first sheath layer 27 may be mechanically bonded to the interior surface of the second sheath layer 26. In various embodiments, the mechanical bond between the first sheath layer 27 and the second sheath layer 26 may be a heat bond that may be formed as the molten polyamide 6 is extruded onto the surface of the first sheath layer 27. The outer sheath may be in contact with the dam paper 28, although the outer sheath may not be mechanically bonded thereto, such that the outer sheath may loosely enclose the dam paper 28 and multiple conductors 2 a, 2 b, 2 c while having a nominally flat cross section corresponding to the nominally flat orientation of the multiple conductors 2 a, 2 b, 2 c. As a non-limiting example, where the multiple conductors 2 a, 2 b, 2 c are arranged such that the center points of each of the multiple conductors are within a single plane, the outer sheath may have a stadium-shape or flat oval cross section. Moreover, in various embodiments, a bare conductor 2 b may be individually enclosed in a paper barrier 29. In various embodiments, the resulting cable does not comprise a dam paper 28, such that the interior surface of the first sheath layer 27 may be in contact with the exterior surface of the multiple conductors 2 a, 2 b, 2 c. In such configurations, the first sheath layer 27 may not be mechanically bonded to the exterior surface of the multiple conductors 2 a, 2 b, 2 c.

In various embodiments, each of the first sheath layer 27 and second sheath layer 26 may have a substantially uniform thickness around the perimeter of the cable (see FIG. 2B-B). For example, the thickness of the second sheath layer 26 may have a 40% tolerance, and more preferably a 20% tolerance, and even more preferably a 17% tolerance. In various embodiments, such a tolerance may correspond to a 2 mil tolerance, and more preferably a 1 mil tolerance around the perimeter of the cable 13. For example, such a tolerance may correspond to a second sheath layer thickness of 6 mils +/−1 mil or 6 mils +/−0.5 mils. As yet other non-limiting examples, such a tolerance may correspond to a second sheath layer thickness of 4 mils +/−1 mil or a second sheath layer thickness of 5 mils +/−1 mil. Similarly, the thickness of the first sheath layer 27 may have a 10% tolerance, and more preferably an 8.25% tolerance. Such a tolerance may correspond to a first sheath layer thickness of 24 mils +/−0.5 mils or a first sheath layer thickness of 24 mils +/−1 mil.

The overall thickness of the combination of the outer sheath and dam paper 28 (if included) may be sufficient to satisfy applicable regulatory requirements or standards established by industry groups (e.g., the Underwriters Laboratory) or other reviewing entities. Alternatively, the outer sheath alone may have a thickness sufficient to satisfy applicable regulatory requirements or standards. As a non-limiting example, the overall thickness of the combination of the outer sheath and the dam paper 28 may be at least 30 mils. Specifically, the second barrier layer 26 may have a thickness between 5-8 mil, but preferably 6 mil, the first barrier layer 27 may have a thickness between 23-25 mil, but preferably 24 mil, and the dam paper 28 may have a thickness of 4 mil. Moreover, as illustrated in detail below, the second sheath layer 26 may have a low dynamic coefficient of friction, and thus a low pulling force is necessary for installation of the cable 13 in an installation site.

Pulling Force Test Apparatus, Methods, and Results

FIGS. 4A and 4B illustrate various components of a pull-force test apparatus that was used to determine the effects on necessary pulling force of incorporating a second sheath layer 26 as described herein into a cable. As illustrated in FIG. 4A, the test apparatus comprises two identical test walls 100 each comprising a 90° corner 101, aligned to form a “U” shape. Each test wall 100 comprises a short wall section 102 and a long wall section 103 adjacent the corner 101. The short wall section comprises 4 vertical studs 110, and the long wall section comprises 7 vertical studs 110. Each of the studs 110 is supported by a support structure comprising a base 121, a top plate 122 and a sole plate 123 collectively configured to maintain the spacing and orientation of the studs 110 relative to one another.

Each stud 110 comprises a 1½″ by 3½″ soft pine board, commonly referred to as a “2×4.” The studs 110 are spaced on 16-inch centers (i.e., spaced such that a 16″ long space exists between the centerline of each stud), and aligned such that the wide-sides (i.e., 3½″ sides) of adjacent studs 110 are in parallel planes. Each stud has a 10″ tall by 1″ wide, stadium shaped test slot 111 extending therethrough in a direction perpendicular to the orientation of the 3½″ side of the stud 110. The vertical centerline of the slot is aligned with the vertical centerline of each corresponding stud 110.

The studs 110 are each configured to support a pulling block 115 as illustrated in FIG. 4B. Each pulling block comprises a 1½″ by 3½″ soft pine board having five, ¾″ diameter test holes 116A-116E extending therethrough in a direction perpendicular to the orientation of the 3½″ side of the pulling block 115. The test holes 116A-116E are arranged on 2″ centers (e.g., spaced such that a 2″ long space exists between the center point of each test hole) and aligned such that the centerline of the 3½ inch side of the pulling block 115 extends through the center point of all five test holes 116A-116E. Moreover, the center point of the center test hole 116C is concentric with the center point of the 3½ inch side of the pulling block 115.

When mounted on a stud 110, the center point of the center test hole 116C of the pulling blocks 115 is concentric with the center point of the test slot 111 of the stud 110. In the illustrated embodiment of FIGS. 4A and 4B, the pulling blocks 115 are each attached to a corresponding stud 110 using bolts secured through corresponding mounting holes of the pulling blocks 115 and studs 110. For each section 102, 103 of the test wall 100, the pulling blocks 115 are mounted to the studs such that the pulling blocks 115 are spaced on 16″ centers (i.e., the pulling blocks 115 each have the same orientation relative to the corresponding studs 110 in relation to the corner 101). Moreover, the pulling blocks 115 are mounted to corresponding studs 110 such that each pulling block 115 is closer to the corner 101 than the corresponding stud 110. In such orientation, the pulling blocks 115 nearest to the corner 101 on each section 102, 103 are adjacent.

The two test walls 100 are arranged in a “U” shape, such that the short section 102 of a first test wall 100 is parallel with the long section 103 of a second test wall 100, and the long section 103 of the first test wall 100 is proximate the short section 102 of the second test wall 100. As arranged, the long section 103 of the first test wall 100 and the short section 102 of the second test wall 100 collectively form an 11-stud wall section. The stud 110le forming the end of the long section 103 of the first test wall 100 is spaced apart from the stud 110se forming the end of the short section 102 of the second test wall 100 such that the pulling blocks 115 associated with the studs 110le, 110se are arranged on a 16″ center.

A section of cable to be tested is threaded through test holes in adjacent pulling blocks 115 through the entire “U”-shaped test apparatus. FIG. 4C is a schematic diagram of a short section 102 of a test wall 100 illustrating how a cable 13 is threaded through the test apparatus. As shown in FIG. 4C, the cable 13 is threaded through alternating test holes 116A-B. In the illustrated example, the cable 13 is threaded through a top-level test hole 116A of a first pulling block 115, then a second-level test hole 116B of a second, adjacent pulling block 115, then a top-level test hole 116A of a third, adjacent pulling block 115. This alternating threading pattern is repeated over the entirety of the test apparatus. FIG. 4C illustrates only a subsection of the entirety of the test apparatus, however the same alternating threading pattern shown in FIG. 4C is repeated throughout the entire test apparatus. The cable 13 is threaded through a pattern of adjacent-level test holes, however any threading pattern utilizing adjacent pattern test holes may be used. As illustrated, the cable may be threaded through holes 116A and 116B, although the cable may alternatively be threaded through holes 116B and 116C; holes 116C and 116D; or holes 116D and 116E. During testing, each test hole is utilized for a single test before the pulling blocks 115 are discarded and replaced.

The cable 13 is pulled through the test apparatus in a test direction from an entrance side to an exit side. A length of cable at least equal in length to the length of cable to be tested is unspooled on the entrance side, such that any increased pulling force attributable to the cable being removed from the spool is minimized. The cable extending beyond the exit side of the test apparatus is secured to a 500-lb load cell (e.g., a Smart S-beam parallel/shear beam load cell), which is secured via a rope to a cable tugger (not shown) located 12 feet away from the exit end of the test apparatus and oriented such that the cable 13 is pulled at least substantially horizontally between the exit side of the test apparatus and the cable tugger. The load cell is in electrical communication with a data recording device (e.g., a computing device) configured to record the amount of force measured by the load-cell. Other load cells, such as a 20-lb Smart S-beam parallel/shear beam load cell, may also be used in the test.

During testing, the cable tugger applies a pulling force to the cable 13 sufficient to pull the cable through the testing apparatus at a uniform rate until a 10-foot long length of cable 13 has been pulled through the test apparatus. The load cell measures the amount of pulling force applied by the cable tugger, and communicates the data to the data recording device. For each test sample type, 3 samples were tested by pulling a 10-foot long length of cable 13 through the test apparatus using the same set of holes in the pulling blocks 115. Using the same set of holes in the pulling blocks 115 substantially recreates the effect of pulling a single long test sample through the testing apparatus. Thus, as additional test samples are pulled through the holes in the pulling blocks 115, the pulling force necessary to pull the sample through the test apparatus decreases. This decrease in necessary pulling force may be attributable to a smoothing of the interior of the holes of the pulling blocks 115 as cable is pulled across the surfaces of the holes, or it may be attributable to residual lubricant being deposited on the surface of the holes of the pulling blocks 115. The amount of force measured by the load cell during each measurement point of the 3 tests for each sample type is averaged to determine an average pulling force necessary to pull the cable through the test apparatus.

The pull test was performed on several 12/2 NM-B cable samples including cables marketed by various companies, cables produced without a second sheath layer 26 as discussed herein, and cables having various levels of additives incorporated into the sheath layer 26. The results of the pull test are summarized in Table 1. These results illustrate that a cable having a second sheath layer 26 as discussed herein requires significantly less pulling-force to install than similar NM-B cables that do not have a second sheath layer 26.

TABLE 1 Measured Average Pulling Sample Type Force (lb.) Company 1 “12/2” cable without a second sheath layer 36.3 Company 2 “12/2” cable without a second sheath layer 64.5 Company 3 “12/2” cable without a second sheath layer 48.0 “12/2” Test Sample 1 having a nylon second sheath layer 19.0 without flame retardant additive and with 12% composition of silicon lubricant “12/2” Test Sample 2 having a nylon second sheath layer 18.0 with 5% composition of flame retardant additive and with 12% composition of silicon lubricant “12/2” Test Sample 3 having a nylon second sheath layer 17.5 with a 10% composition of flame retardant additive and with 12% composition of silicon lubricant

As shown in Table 1, the test samples having a nylon second sheath layer required at least 48% less pulling force than the nearest comparable cable to pull the cable through the test apparatus.

Conclusion

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

That which is claimed:
 1. A process for producing non-circular electrical cable, wherein the non-circular electrical cable comprises one or more conductors arranged in a non-circular arrangement and an exterior sheath comprising a first sheath layer and a second sheath layer, said process comprising steps for: advancing the one or more conductors through an extruder head; extruding a first sheath layer comprising a plastic material around the one or more conductors, wherein the first sheath layer is initially extruded in a substantially circular shape having an inner surface and an exterior surface and at least a portion of the inner surface thereof is spaced from the one or more conductors; extruding a second sheath layer comprising a nylon material around an exterior surface of the first sheath layer, wherein the second sheath layer has a different polymer composition than the first sheath layer; applying a negative pressure to the interior surface of the first sheath layer, thereby pulling the first sheath layer and second sheath layer onto the one or more conductors and into a non-circular shape having a cross section substantially similar to the combined cross section of the one or more conductors; and cooling the first and second sheath layers.
 2. The process of claim 1, wherein the second sheath layer additionally comprises a lubricant for decreasing the pulling force of the non-circular electrical cable.
 3. The process of claim 2, wherein the lubricant comprises a silicon-based lubricant.
 4. The process of claim 2, comprising the additional step of combining the nylon material and lubricant prior to extruding the second sheath layer.
 5. The process of claim 1, wherein the first sheath layer comprises a poly-vinyl chloride material.
 6. The process of claim 5, wherein the first sheath layer comprises a foamed poly-vinyl chloride material.
 7. The process of claim 5, wherein the first sheath layer comprises a re-grind poly-vinyl chloride material.
 8. The process of claim 1, wherein a mechanical bond is formed between the first sheath layer and the second sheath layer.
 9. The process of claim 8, wherein the mechanical bond comprises a heat bond.
 10. The process of claim 1, wherein the one or more conductors comprises a first conductor, a second conductor and a ground wire, wherein the first conductor has a first insulative coating on an external surface of the first conductor and the second conductor has a second insulative coating on an external surface of the second conductor, and wherein the first conductor, second conductor, and ground wire are arranged in a substantially flat configuration. 